A Novel Control Method for Rotary Blood Pumps as Left Ventricular Assist Device Utilizing Aortic Valve State Detection

Current status and future directions in pediatric ventricular assist device

A ventricular assist device (VAD) is a form of mechanical circulatory support that uses a mechanical pump to partially or fully take over the function of a failed heart. In recent decades, the VAD has become a crucial option in the treatment of end-stage heart failure in adult patients. However, due to the lack of suitable devices and more complicated patient profiles, this therapeutic approach is still not widely used for pediatric populations. This article reviews the clinically available devices, adverse events, and future directions of design and implementation in pediatric VADs.

Hybrid Mock Circulatory Loop Simulation of Extreme Cardiac Events

OBJECTIVE

This paper presents preliminary methods of incorporating the pathological conditions of cardiac arrhythmias and valvular stenosis in hybrid mock circulation loop (hMCL) operation for the enhanced verification and validation of mechanical circulatory support devices such as VADs.

METHODS

The MGH/MF Waveform datasets from PhysioNet database (including both nominal and clinically diagnosed arrhythmic ECG measurements) as well as cardiovascular system model updates are used to recreate arrhythmic events and valvular stenosis in vitro.

RESULTS

Preliminary results show the hMCL can recreate each tested cardiac event within 2% and 4% mean error for reference pressure tracking in the aortic and left ventricular pressure chambers, respectively. Further, frequency spectrum analysis comparisons using the magnitude-squared coherence analysis shows close alignment between measured arrhythmic and hMCL realized pressure frequency content.

CONCLUSION

The generation of cardiac arrhythmias and valvular stenosis around a VAD via both model and acute measurement based methods was achieved.

SIGNIFICANCE

Pathological conditions such as cardiac arrhythmias and valvular stenosis are limited in documentation despite the large percentage of patients who experience these events. This paper provides a means to begin incorporating these events into hardware-in-the-loop mock circulatory systems for next generation VAD validation and verification.

Potential of Medical Management to Mitigate Suction Events in Ventricular Assist Device Patients

Ventricular suction is a common adverse event in ventricular assist device (VAD) patients and can be due to multiple underlying causes. The aim of this study is to analyze the potential of different therapeutic interventions to mitigate suction events induced by different pathophysiological conditions. To do so, a suction module was embedded in a cardiovascular hybrid (hydraulic-computational) simulator reproducing the entire cardiovascular system. An HVAD system (Medtronic) was connected between a compliant ventricular apex and a simulated aorta. Starting from a patient profile with severe dilated cardiomyopathy, four different pathophysiological conditions leading to suction were simulated: hypovolemia (blood volume: -900 ml), right ventricular failure (contractility -70%), hypotension (systemic vascular resistance: 8.3 Wood Units), and tachycardia (heart rate:185 bpm). Different therapeutic interventions such as volume infusion, ventricular contractility increase, vasoconstriction, heart rate increase, and pump speed reduction were simulated. Their effects were compared in terms of general hemodynamics and suction mitigation. Each intervention elicited a different effect on the hemodynamics for every pathophysiological condition. Pump speed reduction mitigated suction but did not ameliorate the hemodynamics. Administering volume and inducing a systemic vasoconstriction were the most efficient interventions in both improving the hemodynamics and mitigating suction. When simulating volume infusion, the cardiac powers increased, respectively, by 38%, 25%, 42%, and 43% in the case of hypovolemia, right ventricular failure, hypotension, and tachycardia. Finally, a management algorithm is proposed to identify a therapeutic intervention suited for the underlying physiologic condition causing suction.

An Optimal H-Infinity Controller for Left Ventricular Assist Devices Based on a Starling-like Controller: A Simulation Study

Left ventricular assist devices (LVADs) are emerging innovations that provide a feasible alternative treatment for heart failure (HF) patients to enhance their quality of life. In this work, a novel physiological control system to optimize LVAD pump speed using an H-infinity controller was developed. The controller regulates the calculated target pump flow vs. measured pump flow to meet the changes in metabolic demand. The method proposes the implementation of the Frank–Starling mechanism (FSM) approach to control the speed of an LVAD using the left ventricle end-diastolic volume (Vlved) parameter (preload). An operating point was proposed to move between different control lines within the safe area to achieve the FSM. A proportional–integral (PI) controller was used to control the gradient angle between control lines to obtain the flow target. A lumped parameter model of the cardiovascular system was used to evaluate the proposed method. Exercise and rest scenarios were assessed under multi-physiological conditions of HF patients. Simulation results demonstrated that the control system was stable and feasible under different physiological states of the cardiovascular system (CVS). In addition, the proposed controller was able to keep hemodynamic variables within an acceptable range of the mean pump flow (Qp) (max = 5.2 L/min and min = 3.2 L/min) during test conditions.